Zoom and focusing arrangements are used as suitable arrangements of optical lenses in order suitably to set a focal length of an optical instrument. These can be used to set a magnification that is achievable with the optical instrument. Typically, for this purpose, arrangements of optical elements such as lenses or lens groups are used, of which at least one lens or a lens group is arranged movable along an optical axis of the arrangement. For example, in a suitable arrangement, a movable lens group can be provided for suitable zooming, and a movable lens group for setting the focus. By setting a position of this movable lens in relation to the optical axis, the focal length of the lens system and thus the magnification of the optical instrument is set. Zoom arrangements of this type are used in microscopes, cameras and particularly also in total stations or tachymeters.
Particularly in the field of total stations and tachymeters, a high level of accuracy and reproducibility in setting the position of the movable lens is of great importance. In the design of the relevant lens arrangements, it is necessary to keep tolerances which can arise, for example, from drive motors of the movable lens or a corresponding lens mounting, as small as possible. It has been found inter alia that positional errors of the drive motors in particular can have an influence on the setting accuracy and reproducibility of a desired position if the adjustable lens is to be moved from different starting directions, for example, into a desired reference position. It is therefore desirable inter alia that a movable lens or lens group is always moved from the same direction into the desired position or into a reference position.
Modern zoom and focusing arrangements for use, for example, in total stations or tachymeters are usually very compactly designed. It is thus also desirable that a drive system for a movable lens or a movable lens group enables a compact arrangement of the lenses within such a zoom and focusing arrangement.
An example of a conventional lens mounting is described in the patent application EP 1 510 846 A1. Therein, a guide system for optical systems is described in which lenses or lens groups can be displaced in relation to one another. The system proposed therein has a housing extending along an optical axis in which suitable guide carriages for accommodating optical lenses are arranged. These guide carriages have the form of sleeve segments or cylinder segments which have sliding elements on their outer surfaces lying against corresponding inner guide surfaces of the housing. The sleeve segments proposed therein are at least partially manufactured from a magnetizable material and are guided on the guide surfaces of the housing by the effect of suitable magnetic forces.
A further example of an optical guide system is described in the application WO 2013/135313 A1. Therein, an essentially cylindrical guide carriage for accommodating optical elements and which is guided within a cylindrical housing is proposed. As described therein, the guide carriage is mounted with the aid of pairs of sliding elements of which a pair is adjustable by rotation in order to ensure play-free mounting. The guide carriage is connected via a suitable coupling to a drive, by means of which the guide carriage is displaceable within the housing along an optical axis.
In the application US 2007/0122136 A1, a device for determining the position of a guide carriage within a corresponding housing is disclosed. For this purpose, a sensor in the form of a light barrier is provided at the housing and, at the guide carriage, a suitable interrupter element. The interrupter element is therein arranged such that, on a movement of the guide carriage along the optical axis, the interrupter element interrupts the light barrier so that, for example, a desired reference position of the guide carriage within the housing can be determined using the corresponding signal of the light barrier.
It is an object of the present invention to improve the prior art and to provide an optical guide system with which an optical element such as an optical lens or lens assembly can be reproducibly positioned within a guide housing with a high degree of accuracy and, for example, can be moved into a reference position.